Subsidiary Information (Details 2) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenues
Net earned premiums	$ 225,000,000	$ 211,100,000	$ 230,000,000	$ 254,000,000	$ 286,300,000	$ 288,700,000	$ 297,000,000	$ 314,700,000	$ 920,055,000	$ 1,186,705,000	$ 930,429,000
Net investment income	100,300,000	93,500,000	101,100,000	96,100,000	93,900,000	85,600,000	90,900,000	84,300,000	391,017,000	354,703,000	259,222,000
Net realized investment gains (losses)	(4,600,000)	(11,100,000)	(5,100,000)	2,800,000	(600,000)	(2,400,000)	(8,400,000)	9,400,000	(17,992,000)	(1,994,000)	(32,662,000)
Net change in fair value of credit derivatives:
Realized gains and other settlements									5,959,000	153,495,000	163,558,000
Net unrealized gains (losses)									553,779,000	(155,106,000)	(337,810,000)
Net change in fair value of credit derivatives	(295,200,000)	1,155,900,000	(64,800,000)	(236,200,000)	(129,900,000)	(224,000,000)	73,500,000	278,800,000	559,738,000	(1,611,000)	(174,252,000)
Other income									(33,500,000)	(224,300,000)	(65,600,000)
Total Revenues									1,819,313,000	1,313,453,000	917,159,000
Expenses
Loss and LAE	148,600,000	214,900,000	123,900,000	(25,500,000)	104,800,000	110,800,000	85,700,000	110,900,000	461,890,000	412,161,000	393,800,000
Amortization of deferred acquisition costs	6,700,000	7,300,000	9,500,000	7,400,000	11,000,000	8,000,000	6,900,000	8,200,000	30,849,000	34,057,000	53,899,000
Interest expenses	24,700,000	24,900,000	24,700,000	24,800,000	24,700,000	24,900,000	24,900,000	25,100,000	99,112,000	99,621,000	62,783,000
Goodwill and settlements of pre-existing relationship											23,341,000
Other operating expenses									193,000,000	218,300,000	266,400,000
Total expenses									784,851,000	764,147,000	800,227,000
Income (loss) before income taxes	(146,800,000)	1,056,000,000	(90,300,000)	215,500,000	(312,600,000)	151,600,000	257,000,000	453,300,000	1,034,462,000	549,306,000	116,932,000
Total provision (benefit) for income taxes	(63,200,000)	294,800,000	(47,700,000)	74,900,000	(129,100,000)	(13,000,000)	77,900,000	119,800,000	258,842,000	55,599,000	32,110,000
Net income (loss)	(83,600,000)	761,200,000	(42,600,000)	140,600,000	(183,500,000)	164,600,000	179,100,000	333,500,000	775,620,000	493,707,000	84,822,000
Less: Noncontrolling interest of variable interest entities											(1,156,000)
Net income (loss) attributable to Assured Guaranty Ltd.	(83,600,000)	761,200,000	(42,600,000)	140,600,000	(183,500,000)	164,600,000	179,100,000	333,500,000	775,620,000	493,707,000	85,978,000
Total Shareholders' Equity Attributable to Assured Guaranty Ltd.
Revenues
Net investment income											100,000
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									800,300,000	518,100,000	113,300,000
Total Revenues									800,300,000	518,100,000	113,400,000
Expenses
Other operating expenses									24,700,000	24,400,000	27,400,000
Total expenses									24,700,000	24,400,000	27,400,000
Income (loss) before income taxes									775,600,000	493,700,000	86,000,000
Net income (loss)									775,600,000	493,700,000	86,000,000
Net income (loss) attributable to Assured Guaranty Ltd.											86,000,000
AGUS (Issuer)
Revenues
Net investment income											500,000
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									644,000,000	454,300,000	310,000,000
Total Revenues									644,000,000	454,300,000	310,500,000
Expenses
Interest expenses									39,400,000	39,300,000	31,600,000
Other operating expenses									700,000	3,300,000	18,800,000
Total expenses									40,100,000	42,600,000	50,400,000
Income (loss) before income taxes									603,900,000	411,700,000	260,100,000
Total provision (benefit) for income taxes									(14,000,000)	(14,900,000)	(15,800,000)
Net income (loss)									617,900,000	426,600,000	275,900,000
Net income (loss) attributable to Assured Guaranty Ltd.											275,900,000
AGMH
Revenues
Net investment income									700,000	500,000	300,000
Net realized investment gains (losses)										100,000
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									404,600,000	530,600,000	736,000,000
Total Revenues									405,300,000	531,200,000	736,300,000
Expenses
Interest expenses									53,600,000	53,600,000	26,800,000
Other operating expenses									1,100,000	2,800,000	2,500,000
Total expenses									54,700,000	56,400,000	29,300,000
Income (loss) before income taxes									350,600,000	474,800,000	707,000,000
Total provision (benefit) for income taxes									(18,900,000)	(21,100,000)	(10,100,000)
Net income (loss)									369,500,000	495,900,000	717,100,000
Net income (loss) attributable to Assured Guaranty Ltd.											717,100,000
Other Subsidiaries
Revenues
Net earned premiums									904,100,000	1,168,200,000	895,200,000
Net investment income									405,300,000	369,200,000	259,400,000
Net realized investment gains (losses)									(18,000,000)	(6,100,000)	(32,900,000)
Net change in fair value of credit derivatives:
Realized gains and other settlements									6,000,000	153,500,000	163,600,000
Net unrealized gains (losses)									553,700,000	(155,100,000)	(337,800,000)
Net change in fair value of credit derivatives									559,700,000	(1,600,000)	(174,200,000)
Equity in earnings of subsidiaries									617,900,000	426,600,000	275,900,000
Other income									(28,900,000)	(223,200,000)	(52,900,000)
Total Revenues									2,440,100,000	1,733,100,000	1,170,500,000
Expenses
Loss and LAE									453,700,000	406,400,000	395,100,000
Amortization of deferred acquisition costs									50,600,000	41,700,000	18,100,000
Interest expenses									21,100,000	21,700,000	4,900,000
Goodwill and settlements of pre-existing relationship											(147,100,000)
Other operating expenses									175,000,000	190,000,000	255,300,000
Total expenses									700,400,000	659,800,000	526,300,000
Income (loss) before income taxes									1,739,700,000	1,073,300,000	644,200,000
Total provision (benefit) for income taxes									279,000,000	79,600,000	51,400,000
Net income (loss)									1,460,700,000	993,700,000	592,800,000
Less: Noncontrolling interest of variable interest entities											(1,200,000)
Net income (loss) attributable to Assured Guaranty Ltd.											594,000,000
Consolidating Adjustments
Revenues
Net earned premiums									16,000,000	18,500,000	35,200,000
Net investment income									(15,000,000)	(15,000,000)	(1,100,000)
Net realized investment gains (losses)										4,000,000	200,000
Net change in fair value of credit derivatives:
Equity in earnings of subsidiaries									(2,466,800,000)	(1,929,600,000)	(1,435,200,000)
Other income									(4,600,000)	(1,100,000)	(12,700,000)
Total Revenues									(2,470,400,000)	(1,923,200,000)	(1,413,600,000)
Expenses
Loss and LAE									8,200,000	5,800,000	(1,300,000)
Amortization of deferred acquisition costs									(19,700,000)	(7,600,000)	35,800,000
Interest expenses									(15,000,000)	(15,000,000)	(500,000)
Goodwill and settlements of pre-existing relationship											170,400,000
Other operating expenses									(8,500,000)	(2,200,000)	(37,600,000)
Total expenses									(35,000,000)	(19,000,000)	166,800,000
Income (loss) before income taxes									(2,435,400,000)	(1,904,200,000)	(1,580,400,000)
Total provision (benefit) for income taxes									12,700,000	12,000,000	6,600,000
Net income (loss)									(2,448,100,000)	(1,916,200,000)	(1,587,000,000)
Net income (loss) attributable to Assured Guaranty Ltd.											$ (1,587,000,000)